<div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Jun 14, 2017 at 4:18 PM, FERNANDO FREDIANI <span dir="ltr"><<a href="mailto:fernando.frediani@upx.com" target="_blank">fernando.frediani@upx.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
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<p>I normally assume that any performance gain from directlly
attaching a LUN to a Virtual Machine then using it in the
traditional way are so little to compensate the extra hassle to do
that. I would avoid as much as I cacn use it, unless it is for
some very special reason where you cannot do in any other way. The
only real usage for it so far was Microsoft SQL Server Clustering
requirements.</p></div></blockquote><div><br></div><div>I tend to agree (from performance perspective), though I don't have numbers to back it up. It probably doesn't matter that much.</div><div>There are however other reasons to use a direct LUN - use of storage-side features, such as replication, QoS, encryption, compression, etc. that you may wish to apply (or disable) per storage.</div><div>Also, there are some strange SCSI commands that some strange applications need that require direct LUN and SCSI pass-through. Clustering (via SCSI reservations is certainly the first and foremost but not the only one).</div><div>Y.</div><div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div bgcolor="#FFFFFF" text="#000000"><p><span class="HOEnZb"><font color="#888888"><br>
</font></span></p><span class="HOEnZb"><font color="#888888">
<p>Fernando<br>
</p></font></span><div><div class="h5">
<br>
<div class="m_-4241215767378892379moz-cite-prefix">On 14/06/2017 03:23, Idan Shaby wrote:<br>
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<div>
<div>Direct luns are disks that are not managed by oVirt.
Ovirt communicates directly with the lun itself, without
any other layer in between (like lvm in image disks).<br>
</div>
</div>
The advantage of the direct lun is that it should have better
performance since there's no overhead of another layer in the
middle.<br>
</div>
The disadvantage is that you can't take a snapshot of it (when
attached to a vm, of course), can't make it a part of a
template, export it, and in general - you don't manage it.<br>
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<div dir="ltr">
<div><br>
Regards,<br>
</div>
Idan<br>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
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<div class="gmail_quote">On Mon, Jun 12, 2017 at 10:10 PM,
Stefano Bovina <span dir="ltr"><<a href="mailto:bovy89@gmail.com" target="_blank">bovy89@gmail.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">Thank you very much.
<div>What about "direct lun" usage and database example?</div>
<div>
<div class="m_-4241215767378892379h5">
<div><br>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">2017-06-08 16:40
GMT+02:00 Elad Ben Aharon <span dir="ltr"><<a href="mailto:ebenahar@redhat.com" target="_blank">ebenahar@redhat.com</a>></span>:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">Hi,
<div>Answer inline<br>
<div class="gmail_extra"><br>
<div class="gmail_quote"><span>On Thu,
Jun 8, 2017 at 1:07 PM, Stefano
Bovina <span dir="ltr"><<a href="mailto:bovy89@gmail.com" target="_blank">bovy89@gmail.com</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">
<div>Hi,</div>
<div>does a storage best
practise document for oVirt
exist?</div>
<div><br>
</div>
<div><br>
</div>
<div>Some examples:</div>
<div><br>
</div>
<div>oVirt allows to extend an
existing storage domain: Is it
better to keep a 1:1 relation
between LUN and oVirt storage
domain?</div>
</div>
</blockquote>
</span>
<div>What do you mean by 1:1 relation?
Between storage domain and the
number of LUNs the domain reside
on? </div>
<span>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">
<div>If not, is it better to
avoid adding LUNs to an
already existing storage
domain?</div>
</div>
</blockquote>
</span>
<div>No problems with storage domain
extension.</div>
<span>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">
<div><br>
</div>
<div>Following the previous
questions:</div>
<div><br>
</div>
<div>Is it better to have 1 Big
oVirt storage domain or many
small oVirt storage domains?</div>
</div>
</blockquote>
</span>
<div>Depends on your needs, be aware
to the following:</div>
<div>- Each domain has its own
metadata which allocates ~5GB of the
domain size.</div>
<div>- Each domain is being
constatntly monitored by the system,
so large number of domain can
decrease the system performance.</div>
<div>There are also downsides with
having big domains, like less
flexability </div>
<span>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">
<div>There is a max num VM/disks
for storage domain?</div>
<div><br>
</div>
<div><br>
</div>
<div>In which case is it better
to use "direct attached lun"
with respect to an image on an
oVirt storage domain? </div>
</div>
</blockquote>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">
<div> </div>
</div>
</blockquote>
</span>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span>
<div dir="ltr">
<div><br>
</div>
<div>Example:</div>
<div><br>
</div>
<div>Simple web server:
----> image</div>
<div>Large database (simple
example):</div>
<div> - root,swap etc: 30GB
----> image?</div>
<div> - data disk: 500GB
-----> (direct or image?)</div>
<div><br>
</div>
<div>Regards,</div>
<div><br>
</div>
<div>Stefano</div>
</div>
<br>
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